Here is the full list of all 12 MONMUSU achievements. It takes around 4-5 hours to unlock all of the achievements on Windows.
Collect all kinds of units
Earn a total of one million gold
Summon 9 monster girls
Summon Kobold
Summon Harpy
Summon Slime
Summon Scylla
Summon Centaur
Summon Arlaune
Summon Lamia
Summon Demon
Summon FoxSpirit